Method for the production of microcrystallines of chloramphenicol



3,543,293 METHOD FOR THE PRODUCTION OF MICRO- CRYSTALLTNES F CHLORAMPHENICOL Saburo Akagi, Katsuaki Matsni, Yoshitsugu Takahashi, and Ryuzo Okada, Tokyo, Japan, assignors to Sankyo Company Limited, Tokyo, Japan No Drawing. Continuation-impart of application Ser. No. 607,377, Jan. 5, 1967. This application Dec. 4, 1968, Ser. No. 781,266 Claims priority, application Japan, Jan. 10, 1966, 41/961 Int. (ll. C07c 103/30 US. Cl. 260-562 6 Claims ABSTRACT OF THE DISCLOSURE Method of producing microcrystallines of chloramphenicol. A solution of chloramphenicol in a water-miscible organic solvent is mixed, under vigorous agitation, with a solution of polyvinylpyrrolidone in water.

CROSS-REFERENCE TO PRIOR APPLICATIONS This is a continuation-in-part of our copending application Ser. No. 607,377, filed on Jan. 5, 1967, now abandoned.

SUMMARY OF THE INVENTION This invention relates to an improvement in the particle size distribution of chloramphenicol crystals. More particularly, it is concerned with a new and improved method for the production of microcrystallines of chloramphenicol.

Chloramphenicol is one of the well known antibiotics and is widely employed for chemotherapeutic purposes. It may be satisfactorily administered in various dosage forms such as tablets, powders, granules, suspensions, syrups, ointments and the like. Depending mainly upon the kind and severity of infection, this antibiotic is most frequently and conveniently employed in the form of an intramuscularly injectable aqueous Suspension. In the preparation of such a suspension, it is advantageous and prefered to employ chloramphenicol crystals in a finely divided form, for example, with a particle size distribution of about 0.5 to 50 The prior art micro powders of chloramphenicol, which have been obtained by utilizing mechanical grinding of chloramphenicol crystals, have a relatively large particle size. This mechanical processing has, moreover, a most serious drawback, since it is difficult, if not impossible, to obtain finely divided crystals with a uniform particle size distribution.

In accordance with this invention, it has been found that microcrystallines of chloramphenicol of superior characteristics are obtained by mixing two solutions, to wit, a first solution of chloramphenicol in a water-misci ble organic solvent and a second solution of polyvinylpyrrolidone in water, the mixing to be effected under vigorous agitation.

It is, therefore, an object of this invention to provide a new and improved method for the production of microcrystallines of chloramphenicol with a uniform particle size distribution, which are of great value, particularly for the purpose of preparing intramuscularly injectable aqueous suspensions.

Other objects will appear hereinafter.

In accordance with this invention there is thus provided a method for the production of microcrystallines of chloramphenicol which comprises mixing a solution of chloramphenicol in a water-miscible organic solvent with a solution of polyvinylpyrrolidone in Water under vigorous agitation.

nited States Patent 3,543,293 Patented Nov. 24, 1970 The term agitation as used herein means agitation carried out with a force sufficient to prevent the growth and aggregation of chloramphenicol crystals. Such agitation may be effected with conventional mechanical means.

In carrying out the procedure of this invention, the agitation should thus be sufiiciently strong so as to prevent the growth and aggregation of chloramphenicol crystals. Any of the known mechanical agitation means, including various conventional agitators or stirrers, may be employed for this purpose. Magnetic stirrers, paddle agitators, propeller type agitators, turbine type agitators, gas blowing, flow mixers, helical type agitators, spiral type agitators as well as ultrasonic generators may all successfully be employed to effect the desired agitation. The agitation force per unit volume should preferably be 3-20 horse powers per 1,000 gallons. Ultrasonic agitation is, however, preferred since it yields the best result. By employing ultrasonic waves, advantageously of about 19-50 kilocycles, preferably of about 25-35 kilocycles, excellent results are obtained which are combined with such advantages as simple performance characteristics, inexpensive equipment requirements and simple large scale processing. Further, uniform microcrystallines are obtaiud. The manner for mixing the chloramphenicol solution and the polyvinylpyrrolidone solution is not critical, but it is usual to add the chloramphenicol solution to the polyvinylpyrrolidone solution.

Preferred examples of water-miscible organic solvents to be employed in this invention include water-miscible monohydric lower aliphatic saturated alcohols, e.g., methanol, ethanol, propanol, sec.-amyl alcohol, tert.- butanol; water-miscible dihydric lower aliphatic saturated alcohols and homopolymers thereof, e.g., ethylene glycol, propylene glycol, butylene glycol, and polyethylene glycol; water-miscible lower aliphatic saturated ketones, e.g. acetone, methylethylketone; water-miscible aliphatic saturated keto alcohols, e.g. diacetone alcohol; water-miscible lower alkyl ethers of dihydric lower aliphatic saturated alcohol and lower alkyl esters thereof, e.g. ethylene glycol monomethyl ether, monopropyl ether, dimethyl ether, and diethylether and diethylene glycol monoethyl ether acetate; water-miscible cyclic ethers, e.g. dioxane, tetrahydrofuran, dioxalane, and tetrahydrofurfuryl alcohol and glycolate and levulinate thereof; water-miscible aliphatic saturated carboxylic acids and water-miscible lower alkyl esters thereof, e.g. formic acid, acetic acid, propionic acid, valeric acid, butyric acid, 3-methoxy butyric acid, methyl and ethyl formates, methyl acetate, and S-methoxybutyl acetate; water-miscible alkylamines, e.g. diisopropyl amine and tripropylamine; water-miscible aliphatic saturated hydroxy acids and lower alkyl esters thereof, e.g. lactic acid and methyl and ethyl lactates; water-miscible lower alkanol amines, e.g., monoethanol amine, diethanol amine,

The molecular weight of the polyvinylpyrrolidone is not a critical feature of this invention, but it is preferred to employ polyvinylpyrrolidone with a molecular weight of about l0,000-750,000. Also, the concentrations of the polyvinylpyrrolidone to be employed are not critical, but a solution of polyvinylpyrrolidone with a concentration of about 0.1-1.0% is advantageously employed in this invention. It has also been found that finer microcrystallines of chloramphenicol can be obtained by utilizing an aqueous solution of polyvinylpyrrolidone which additionally contains a commercially available surface-active agent, for example, Hyamine 1622 (trade name of one of the cationic surface active agents manufactured and sold by Rohm & Haas Co., USA, benzethonium chloride), Tween 40 (trade name of one of the Tween products manufactured and sold by Atlas Powder Co., U.S.A., polyoxyethylene (20) sorbitan monopalmitate), Myrj 52 (trade name of one of the Myrj products manufactured and sold by Atlas Powder Co., U.S.A., polyoxyethylene (40) stearate); methyl cellulose and carboxymethyl cellulose; or polyvinyl alcohol in a suitable amount, for example, in an amount of about based upon the weight of polyvinylpyrrolidone present in the solution.

The mixing and agitation may be generally conducted at a relatively low temperature and is preferably conducted below room temperature. A temperature range of about 3-l0 C. is preferred but higher temperatures may be satisfactorily applied if necessary.

After completion of the agitation, the crystals precipitate in situ and are collected by a conventional means, for example, by centrifugal separation from the resulting suspension, followed by drying.

The following examples are given only for the purpose of illustrating of this invention and should not be construed as limiting the scope thereof.

EXAMPLE 1 Into a 200-ml. beaker containing 100 ml. of water was added 0.5 g. of polyvinylpyrrolidone (molecular weight 38,000) and the resulting solution was cooled to 3 C. A solution of 3 g. of chloramphenicol in 9 ml. of methanol, which solution had been cooled at 3 C., was then added. During the addition, continuous agitation of the mixture was maintained by means of a magnetic stirrer. The mixture first emulsified and then crystals precipitated out gradually. The crystallization was completed in about 1 /2 hours. The precipitated crystals wer collected by means of a centrifugal separator and dried to yield microcrystallines of chloramphenicol with a particle size of 2 1..

The procedure set forth above was repeated several times with dilferent solvents for the chloramphenicol. The methanol was thus replaced by equivalent amounts of one of the following solvents: ethanol, n-propanol, ipropanol, ethylene glycol monomethyl ether, acetone, methylethylketone, dioxane, tetrahydrofuran, acetic acid lactic acid monoethanol amine, diethenol amine, N,N-dimethyl acetoamide, pyridine, pyrrolidone, N-methylpyrrolidone and dimethylsulfoxide. In each case, microcrystallines of chloramphenicol with substantially the same order of particle sizes as described above were obtained.

EXAMPLE 2 Into a 200-ml. beaker containing 100 ml. of water were added 0.5 g. of polyvinylpyrrolidone (molecular weight 38,000) and 0.05 g. of Hyamine 1622 and the resulting solution was cooled to 3 C. To the cooled solution was added a solution of 3 g. of chloramphenicol in 9 ml. of methanol. The methanolic solution had been cooled to 3 C. The mixture was maintained under continuous agitation by means of ultrasonic waves of 28 kilocycles generated by an ultrasonic generator. The mixture was at first emulsified and then crystals precipitated out. The crystallization was completed in about 2 minutes. The precipitated crystals were collected by means of a centrifugal separator and dried to yield microcrystallines of chloramphenicol with a particle size distribution of 1-2,u..

EXAMPLE 3 Into a 200ml. beaker containing ml. of water were added 0.5 g. of polyvinylpyrrolidone (molecular weight 38,000) and 0.05 g. of"Hyamine 1622. The resulting solution was cooled to 3 C. To the cooled solution was then added a solution of 3 g. of chloramphenicol in 12 ml. of propyleneglycol at 3 C. The resulting mixture was kept under continuous agitation with ultrasonic waves of 28 kilocycles. The mixture was at first emulsified and then crystals precipitated out. The crystallization was completed in about 10 minutes. The precipitated crystals were collected by means of a centrifugal separator and dried to yield microcrystallines of chloramphenicol with a particle size distribution of 23,u..

The above procedure was repeated several times, except that in each case 2.5 g. of chloramphenicol were dissolved in 9 ml. of one of the following solvents: amino alcohol, diacetone alcohol and morpholine. Microcrystallines of chloramphenicol with substantially the same order of particle sizes as described above were obtained in each case.

EXAMPLE 4 In a 20-ml. beaker, 1.0 g. of polyvinylpyrrolidone (molecular weight 38,000) and 0.1 g. of Hyamine 1622 were dissolved in 100 ml. of water and the resulting solution was cooled to 3 C. To the cooled solution was added a solution of 3 g. of chloramphenicol in 9 ml. of Polyethylene Glycol 400 (as prescribed in The Pharmacopoeia of Japan, 7th Ed. 1961), which solution had previously been cooled to 3 C. The mixture was kept under continuous agitation with ultrasonic waves of 28 kilocycles. The mixture first emulsified and then crystals precipitated out. The crystallization was completed in about 20 minutes. The precipitated crystals were collected by means of a centrifugal separator and dried to yield microcrystallines of chloramphenicol with a particle size distribution of l-2p..

What is claimed is:

1. A method for the production of microcrystallines of chloramphenicol, which comprises mixing a solution of chloramphenicol in a water-miscible organic solvent which is liquid at an ambient temperature of about 1060 C. with a solution of polyvinylpyrrolidone in water under vigorous agitation, said agitation being sulficiently strong so as to prevent the growth and aggregation of chloramphenicol crystals.

2. The method according to claim 1, wherein said watermiscible solvent is methanol.

3. The method according to claim 1, wherein the polyvinylpyrrolidone has a molecular weight of about 10,000- 750,000.

4. The method according to claim 1, wherein said agitation is carried out with a force per unit volume of about 3 to 20 horse powers/ 1,000 gallons.

5. The method according to claim 1, wherein said agitation is of a strength resulting from an ultrasonic wave of about 19 to 50 kilocycles.

6. The method as claimed in claim 1, wherein the concentration of the aqueous polyvinylpyrrolidone solution is about 0.1-1.0%.

References Cited UNITED STATES PATENTS 2,983,755 5/1961 Kollonitsch et al. 260562 HENRY R. JILES, Primary Examiner H. I. MOATZ, Assistant Examiner US. Cl. X.R. 260--707 

